WIP: Stop autoplaying videos from media pages

Attempts to resolve sentry issue referenced in #1780 (closed)

Not totally clear on what's causing the problem. Seems to happen most reliably when I select 720p quality from video player controls on media pages - but only for some videos.

If I turn off autoplay, I stop getting the related error "Uncaught (in promise) DOMException" so am hoping that it also stops the "UnhandledRejection: Non-Error promise rejection captured with keys: [object has no keys]" as well.